Salt tectonics of the offshore Tarfaya Basin, Moroccan Atlantic margin

Abstract

Salt tectonics play a critical role on passive margins evolution controlling aspects like structural style, subsidence patterns and thermal history, amongst others. The salt-bearing Atlantic passive margin of Morocco hosts one of the oldest stratigraphic records documenting the opening history of the Central Atlantic. However, the available seismic data is scarce and some offshore basins are still poorly studied, particularly in southern Morocco. Through the interpretation of an unpublished 2D/3D seismic dataset from the offshore Tarfaya Basin (SW Morocco), this study aims to highlight the key events that conditioned the evolution of this salt-bearing basin. From proximal to distal regions, the structural style of the basin is characterized by expulsion rollovers and salt-cored anticlines delimited by primary welded surfaces, evolving to buried salt sheets surrounded by thick minibasins and finally, diapirs actively deforming the modern seabed. From Late Triassic to Early Jurassic times, salt was deposited with a basinward thickening wedge-shaped geometry on a narrow trough developed over thinned continental crust. During the Jurassic, sedimentation and associated salt withdrawal triggered early salt deformation. Gravity gliding is a common process in salt-bearing passive margins that requires an originally continuous autochthonous salt layer with a minimum slope angle and longitude to thickness ratio of the overburden. However, in the Tarfaya Basin, the narrow geometry of the salt-bearing depocenter hampered this process. Early salt tectonics was probably triggered by slope progradation during the Early Jurassic. During the Early Cretaceous, the progradation of the Tan-Tan Delta promoted a continued basinward expulsion of salt, the development of a local salt-detached gravitational system and the proximal extrusion of salt sheets. Finally, from Late Cretaceous to the Present-day, shortening related to the convergence between Africa and Eurasia resulted in thick-skin inversion and the rejuvenation of precursor salt structures.